A well-known type of-signal recording and/or reproducing apparatus, for example, a digital audio tape recorder (DAT) using a rotary head, converts an analog signal into a digital signal and records the digital signal on a recording medium, such as a magnetic tape, and reproduces the digital signal recorded on the recording medium and converts and outputs the digital signal into an analog signal.
Such an apparatus adjusts an analog signal like an audio signal to a certain signal level through an analog volume control circuit, converts the adjusted analog signal into a digital signal, and then records the digital signal on a magnetic tape.
Furthermore, in order to reproduce the digital signal recorded on the magnetic tape, the signal reproduced from the magnetic tape is converted into an analog signal, adjusted to a certain signal level through the analog volume control circuit and then jed out.
FIG. 1 shows the construction of a signal recording system 1 of a conventional digital signal recording and/or reproducing apparatus. An analog audio signal S1 supplied from a microphone or an external device is input to a line input terminal 3. The analog audio signal S1 input to the line input terminal 3 is supplied to an analog volume control circuit so as to be adjusted to a volume value required by an analog-digital conversion circuit 6 that receives the signal through an amplifying circuit 5.
The analog-digital conversion circuit 6 converts the analog audio signal into a digital audio signal S3. The digital audio signal S3 is output to a recording circuit 7, modulated to a certain recording signal S4, and recorded on a magnetic tape 9 through a magnetic head 8.
FIG. 2 shows the construction of a signal reproducing system 2 of the conventional digital signal recording and/or reproducing apparatus. A digital signal recorded on a magnetic tape 10 is read out by a magnetic head 11, and supplied as a reproduction signal S5 to a reproducing circuit 12.
The reproducing circuit 12 demodulates the reproduction signal S5 to a digital audio signal S6. The digital signal S6 is converted into an analog audio signal S7 by a digital-analog conversion circuit 13, and supplied through an amplifying circuit 14 to an analog volume control circuit 15, which has, for example, a variable resistor and controls the volume by changing the variable resistor.
The analog volume control circuit 15 adjusts the analog audio signal S7 to a volume value desired by the user. A signal S8 output from the analog volume control circuit 15 is amplified by an amplifying circuit 16, and output as an audio signal S9.
However, if the analog audio signal is output through the amplifying circuit 5 and the analog-digital conversion circuit 6 after being set at a volume value desired by the user in the analog volume control circuit 4 shown in FIG. 1, noise components which signal processing circuits of the amplifying circuit 5, the analog-digital conversion circuit 6 and so on naturally contain are superimposed on the input signal S1 and are recorded as the recording signal S4. Thereby, the S/N ratio is lowered when the volume value is made small.
When an audio signal output from the analog volume control circuit 4 is monitored in recording, if a recording volume value is gradually decreased in, for example, a fade-out operation, since a monitor value is decreased with the decrease in the volume value, the input signal cannot be sufficiently monitored.
Furthermore, when an analog audio signal obtained through the digital-analog conversion circuit 13 and the amplifying circuit 14 shown in FIG. 2 is set at a volume value desired by the user in the analog volume control circuit 15 and then jed out, noise components arising from signal processing circuits of the digital-analog conversion circuit 13, the amplifying circuit 14 and so on are superimposed on the output audio signal S8. Therefore, when an audio signal recorded on a particularly low volume level is reproduced while the set volume value of the analog volume control circuit 15 is increased, since noise components arising from signal processing circuits of the digital-analog conversion circuit 13, the amplifying circuit 14 and so on are amplified together with the audio signal, the S/N ratio of the output audio signal S8 is lowered.